This invention relates to emergency breathing apparatus which is intended primarily for use in effecting an escape from a polluted environment such as might arise as a result of natural disasters, industrial accidents, fires, or any situation where toxic substances such as gases, aerosols or powder are present in the atmosphere.
Emergency escape breathing apparatus generally comprises a flexible hood which, in use, is placed over the head, a source of breathable gas, such as compressed air, and a flexible tube passing between the two. In use, a valve is used to open the source of gas which passes up the tube to the hood, where it is breathed by the user. The source is generally designed to give a fairly limited supply of gas, typically lasting just 10 or 15 minutes, but sufficient to enable the user to escape to a place of safety.
The flexible hood normally has a neck seal which surrounds the neck of a wearer and prevents the ingress of the polluted atmosphere into the interior of the hood. The neck seal also permits the escape of gases from the interior of the hood where an increased pressure, greater than atmospheric pressure, tends to build up due to the continued supply of air, or other breathable gas to the hood. The hood may include a separate exhale valve for limiting the gas pressure increase within the hood.
With the device described above, it is known for the breath of someone wearing the hood to be exhaled into the interior of the hood. This tends to increase the proportion of carbon dioxide inside the hood to a level which makes it undesirable for the air inside the hood to be inhaled. This is despite the fact that fresh air is being supplied continually to the interior of the hood and that C02 contaminated air continually escapes from the interior of the hood to the atmosphere. A known method of overcoming this problem is to use a baffle or other physical barrier (which often takes the form of an orinasal mask or half-mask) to provide a confined space around the wearer""s nose and mouth from which exhaled breath is expelled and to which the new air or other breathable gas is supplied. Where the barrier takes the form of an orinasal mask or half-mask, difficulties are often experienced by the wearer in donning the mask and successfully positioning and maintaining the mask correctly, during use.
Once the hood is in place and air is being supplied, the action of inhalation and exhalation tends to cause the hood to expand and contract in a cyclic manner, thus causing almost continuous movement of the hood material. Thus the visorxe2x80x94that part of the hood which is made of transparent flexible material and through which the user looksxe2x80x94is continually moving and this provides a distraction as a result of the varying optical characteristics of the hood. Furthermore, if the user is a spectacle wearer, the movement of the hood material results in an intermittent movement of the spectacles which is irritating to the wearer.
GB-A-2301039 describes a hood for an emergency escape breathing apparatus which utilizes a semi-rigid member incorporated into the fabric of the hood at the front which serves the dual purpose of maintaining the hood away from the wearer""s face as the apparatus is donned and urging the orinasal mask against the user""s face once the hood is in place
In accordance with the present invention there is provided a hood for a breathing apparatus, said hood being formed from a plurality of panels of flexible material, said panels comprising front and rear panels joined by left and right side panels and a top panel, wherein said front and rear panels incorporate stiffening means for rendering the front and rear panels semi-rigid, and wherein the front panel incorporates a transparent portion forming a visor, and connection means for connecting the interior of the hood to a source of breathable gas.
Each panel may be formed of a single sheet of said flexible material which is joined around its edges to adjacent panels to form the hood. However, the number of joins may be reduced by forming two or more adjacent panels from a single sheet of material which is suitably cut and folded or creased to define the individual panels.
It is anticipated that the individual panels of the hood will be principally planar so that the angle between individual panels, when the hood is in its normal xe2x80x9cas wornxe2x80x9d shape is approximately 90xc2x0, thus giving a generally box-like appearance to the hood. The rear panel may also be generally planar, and approximately parallel to the front panel, but may alternatively have a more curved shape to more closely follow the back of a wearer""s head.
The hood thus comprises semi-rigid front and rear panels joined by left and right side panels and a top panel. If the side and top panels are left flexible then the hood can act in the manner of a bellows during the above-mentioned cyclic expansion and contraction when breathing. In other words, the relatively rigid front and back panels tend to keep their shape during inhalation and exhalation, the changes in volume of the hood being taken up by flexure of the side and top panels. This means that the visor, in particular, maintains its shape during use and does not distort. in an embodiment, the visor extends right across the full width of the front panel, and out into the left and right side panels, thus extending the user""s field of vision. In this case, that part of the visor which is formed by the left and right side panels will flex during breathing but, as this is at the periphery of vision, the disadvantageous effects of the flexing will not be too intrusive.
The stiffening means may take any convenient form. For the rear panel a pad of closed cell foam material may be attached to the panel for this purpose. The pad, typically about 1 cm thick, may be attached to the inside surface of the rear panel by adhesive, but preferably the pad is removably located in a suitable pocket or pockets. In the preferred embodiment, the pad includes a depression or through-hole designed to locate the back of the wearer""s head. The use of a foam pad in this way allows the hood to comfortably and effectively fit a reasonable range of head sizes.
A similar pad could be used to stiffen the front panel but, because of the special requirements of the front panelxe2x80x94visor, air fittingsxe2x80x94alternative methods are preferred. In the preferred embodiment, stiffening of the front panel is achieved by means of a pair of stiffening members which are attached to the material of the front panel, one above the visor and one below. The stiffening members extend across a substantial part of the width of the front panel and, in the case of the lower stiffening member, may also have a portion to which the connection means is attached. The stiffening members are made of rigid or semi-rigid material and preferably are resilient. Examples are spring steel or rigid but resilient plastics material.
The stiffening members may be attached to the material of the front panel by any suitable means but a suitably shaped fabric pocket on the inside surface is the preferred method.
In the preferred embodiment, an orinasal mask is fitted on the inside of the front panel immediately behind the gas connection means and is arranged so as to cover the wearer""s nose and mouth during use of the hood. The orinasal mask thus defines a sub-chamber within the hood, although there are connections between the orinasal mask and the hood to allow a limited exchange of gas therebetween.
The underside of the hood may be left open, but it is preferred to provide an elastic neckband which seals around the wearer""s neck to thus define a substantially sealed:interior, when in use, and thus protects the wearer from the surrounding atmosphere, which may not be breathable.